1. Field of the Invention
The present invention relates to control means for automatic transmissions and more particularly to control means for automatic transmissions having a hydraulic torque converter and a multiple-stage transmission gear mechanism connected with the hydraulic torque converter. More specifically, the present invention pertains to control means for determining the gear stage of the transmission gear mechanism in accordance with the vehicle operating condition.
2. Description of the Prior Art
Conventional automatic transmissions generally include a hydraulic torque converter having an output shaft connected with a multiple-stage gear transmission mechanism, such as a planetary gear mechanism. For selecting a desired one of the gear stages, the transmission usually includes a hydraulic system which has hydraulically operated and electromagnetically operated valves for appropriately selecting hydraulic circuits to thereby engage selected ones of friction devices such as clutches and brakes. Where the hydraulic system includes electromagnetically operated solenoid valves, electronic means is generally provided for detecting that the vehicle operating condition has been shifted from one zone to another, crossing a shifting line and producing electric signals for energizing appropriate ones of the solenoid valves.
Generally, such a shifting line is determined in terms of the vehicle speed and the engine load.
It has been known in automatic transmissions of the aforementioned type to provide more than one shift pattern, each having a plurality of shift lines. For example, Japanese patent publication No. 52-182 proposes an automatic transmission control which includes two shift patterns which can be manually selected for governing gear shifting operations, so that the gear mechanism is shifted at a lower vehicle speed under one of the shift patterns than under the other shift pattern. Since the shift pattern wherein the shifting is carried out at a lower vehicle speed can give economical operation, it may be called an economy mode, whereas the other shift pattern may be called a power mode, since it can give a stronger acceleration.
It has been proposed to select the shift pattern automatically in accordance with a vehicle condition. For example, in Japanese patent application No. 54-34643 filed on Mar. 24, 1979, and disclosed for public inspection on Oct. 7, 1980, under the disclosure No. 55-129645, there is disclosed a control system for automatic transmissions wherein the shift pattern is switched to the economy mode when the fuel quantity decreases below a predetermined level. It should, however, be noted that in the known control systems, accelerating characteristics cannot substantially be changed by selectively switching the shifting pattern from one to another. Particularly in the vehicle starting period, the transmission gear mechanism is in the first stage both in the power mode and the economy mode, so that there will be no difference in acceleration between the two modes.